1. Field of the Invention
One embodiment of the present invention relates to a film, an element, a formation method of a film, or a manufacturing method of an element.
Note that one embodiment of the present invention is not limited to the above technical field. The technical field of one embodiment of the invention disclosed in this specification and the like relates to an object, a method, or a manufacturing method. In addition, one embodiment of the present invention relates to a process, a machine, manufacture, or a composition of matter. Specifically, examples of the technical field of one embodiment of the present invention disclosed in this specification and the like include a semiconductor device, a display device, a liquid crystal display device, a light-emitting device, a lighting device, a power storage device, a memory device, an input device, an input/output device, a method for driving any of them, and a method for manufacturing any of them.
2. Description of the Related Art
Graphene is a one-atom-thick sheet of sp2-bonded carbon atoms that form a honeycomb-like hexagonal lattice structure. Strictly speaking, graphene is as defined above; however, in this specification, a carbon film consisting of a plurality of (2 to 100) such sheets stacked is also referred to as graphene.
Graphene is made by a variety of methods; the Hummers method is a simple method and has been used in many researches (see Patent Documents 1 and 2). In the Hummers method, graphite is oxidized with an oxidizer, first. Potassium permanganate is used as the oxidizer, and an acid such as a sulfuric acid is generally added together to promote an oxidation effect.
The oxidized graphite (graphite oxide) retains the layered structure, in which the interlayer distance is, however, larger than that of graphite; thus, the layered structure can be easily broken by ultrasonic treatment or the like, whereby oxidized graphene (graphene oxide) can be obtained. The resulting graphene oxide may have at least one sheet of carbon atoms.
When the graphene oxide is deposited on an appropriate object surface in the form of a thin film shape and reduced, an extremely thin carbon film (graphene) can be formed.